Support subtype-registered meta keys in cache invalidation lookup

Search across all registered subtypes when the caller does not provide
one, so that keys registered for a specific post type are still found
by wp_cache_set_posts_last_changed which only has the meta key.

Adds tests for subtype registration.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: ellatrix

src/wp-includes/meta.php

@@ -1664,6 +1664,8 @@ function registered_meta_key_exists( $object_type, $meta_key, $object_subtype =
  * @return bool True if the meta key invalidates query caches, false otherwise.
  */
 function wp_meta_key_invalidates_query_cache( $object_type, $meta_key, $object_subtype = '' ) {
+	global $wp_meta_keys;
+
 	$meta_keys = get_registered_meta_keys( $object_type, $object_subtype );
 
 	if ( isset( $meta_keys[ $meta_key ] ) ) {
@@ -1678,6 +1680,15 @@ function wp_meta_key_invalidates_query_cache( $object_type, $meta_key, $object_s
 		}
 	}
 
+	// When no subtype is given, search across all registered subtypes.
+	if ( '' === $object_subtype && is_array( $wp_meta_keys ) && isset( $wp_meta_keys[ $object_type ] ) ) {
+		foreach ( $wp_meta_keys[ $object_type ] as $registered_keys ) {
+			if ( isset( $registered_keys[ $meta_key ] ) ) {
+				return $registered_keys[ $meta_key ]['invalidates_query_cache'];
+			}
+		}
+	}
+
 	// Unregistered keys default to invalidating caches.
 	return true;
 }

tests/phpunit/tests/meta/invalidatesQueryCache.php

@@ -21,6 +21,7 @@ public static function wpTearDownAfterClass() {
 
 	public function tear_down() {
 		unregister_meta_key( 'post', 'nocache_meta' );
+		unregister_meta_key( 'post', 'nocache_meta', 'post' );
 		unregister_meta_key( 'post', 'normal_meta' );
 		parent::tear_down();
 	}
@@ -193,4 +194,50 @@ public function test_meta_query_allows_regular_key() {
 
 		$this->assertStringContainsString( 'some_regular_key', $sql['where'], 'Regular meta key should appear in WHERE clause.' );
 	}
+
+	/**
+	 * A key registered for a specific post type should skip cache invalidation.
+	 */
+	public function test_subtype_registration_skips_cache_invalidation() {
+		register_post_meta(
+			'post',
+			'nocache_meta',
+			array( 'invalidates_query_cache' => false )
+		);
+
+		wp_cache_set_last_changed( 'posts' );
+		$before = wp_cache_get_last_changed( 'posts' );
+
+		usleep( 1000 );
+		add_post_meta( self::$post_id, 'nocache_meta', 'value1' );
+
+		$after = wp_cache_get_last_changed( 'posts' );
+		$this->assertSame( $before, $after, 'last_changed should not change for non-cacheable meta registered on a specific post type.' );
+	}
+
+	/**
+	 * A key registered for a specific post type should be refused in meta queries.
+	 *
+	 * @expectedIncorrectUsage WP_Meta_Query::get_sql_for_clause
+	 */
+	public function test_subtype_registration_refuses_meta_query() {
+		register_post_meta(
+			'post',
+			'nocache_meta',
+			array( 'invalidates_query_cache' => false )
+		);
+
+		$meta_query = new WP_Meta_Query(
+			array(
+				array(
+					'key'   => 'nocache_meta',
+					'value' => 'test',
+				),
+			)
+		);
+
+		$sql = $meta_query->get_sql( 'post', 'wp_posts', 'ID' );
+
+		$this->assertStringNotContainsString( 'nocache_meta', $sql['where'], 'Non-cacheable meta key should not appear in WHERE clause.' );
+	}
 }